Made a sentence slightly more english

Replaced "Even more" with "What's more" to make a sentence "more english".

Author: GTheron

components/http_foundation/introduction.rst

@@ -430,7 +430,7 @@ represented by a PHP callable instead of a string::
     you must call ``ob_flush()`` before ``flush()``.
 
     Additionally, PHP isn't the only layer that can buffer output. Your web
-    server might also buffer based on its configuration. Even more, if you
+    server might also buffer based on its configuration. What's more, if you
     use fastcgi, buffering can't be disabled at all.
 
 .. _component-http-foundation-serving-files: